International audienceThe winter of 2012 experienced peculiar atmospheric conditions that triggered a massive formation of dense water on the continental shelf and in the deep basin of the Gulf of Lions. Multiplatforms observations enabled a synoptic view of dense water formation and spreading at basin scale. Five months after its formation, the dense water of coastal origin created a distinct bottom layer up to a few hundreds of meters thick over the central part of the NW Mediterranean basin, which was overlaid by a layer of newly formed deep water produced by open-sea convection. These new observations highlight the role of intense episodes of both dense shelf water cascading and open-sea convection to the progressive modification of the NW Mediterranean deep waters

Summer repeated hydrographic surveys and 4 years of mooring observations are used to characterize for the first time the interannual variability of the bottom water in the Mertz Glacier Polynya (MGP) on the East Antarctic shelf (142 E-146 E). Until 2010, large interannual variability was observed in the summer bottom salinity with year-to-year changes reaching 0.12 in Commonwealth Bay, the region with the highest sea ice production. The summer variability was shown to be linked to the efficiency of the convection during the preceding winter. The recent freshening of the bottom waters subsequent to the Mertz Glacier calving was well beyond the range of the precalving interannual variability. Within 2 years after the event, the bottom water of the shelf became too light to possibly contribute to renewal of the Antarctic Bottom Water. Rough estimates of the freshwater budget of the Ad elie Depression indicate that the freshening necessary to compensate for net sea ice production in the MGP did not change drastically after the Mertz calving. The year-to-year salinity changes appeared to respond to the MGP activity. Yet, prior to the calving, the convective system in the polynya was also partly controlled by the late winter bottom salinity through a mechanism leading to a sequence of alternatively fresher and more saline bottom waters over the period [2007][2008][2009][2010]. Exceptional events like the Mertz calving seem to be able to switch over the system into a less stratified state where convection responds more directly to changes in the surface forcing. IntroductionAntarctic Bottom Water (AABW), the densest water mass of the world ocean, occupies the abyssal layer of the Southern Ocean as a relatively well-oxygenated, cold and fresh product, which spreads north into the Atlantic, Indian, and Pacific oceans. Surface water transformation on the continental margins around Antarctica and subsequent sinking of the dense shelf waters along the slope supply the bottom limb of the ocean thermohaline circulation. It has been argued that changes in the properties or formation rate of the AABW could affect the strength of the thermohaline circulation, and therefore the global climate [Stouffer et al., 2007;Purkey and Johnson, 2012].The production of AABW is considered to originate on the Antarctic shelf in coastal polynyas where nearfreezing water (the so-called High-Salinity Shelf Water, HSSW) is formed through ocean surface cooling and brine drainage from growing sea ice. Upon mixing with ambient waters on the shelf and subsequent sinking and entrainment of Circumpolar Deep Water down the continental slope, these waters eventually acquire final AABW properties when reaching the abyssal layer of the Southern Ocean. While this process is suspected to occur at many locations around Antarctica, observations have unambiguously identified some primary formation sites: the Weddell Sea, the Ross Sea [Carmack, 1977], and the Ad elie-George V Land [Gordon and Tchernia, 1972;Rintoul, 1998]. Estimates of the relative im...

The present article describes a new and efficient method of Real Time Kinematic (RTK) Global Navigation Satellite System (GNSS) assisted terrestrial Structure-from-Motion (SfM) photogrammetry without the need for Ground Control Points (GCPs). The system only requires a simple frame that mechanically connects a RTK GNSS antenna to the camera. The system is low cost, easy to transport, and offers high autonomy. Furthermore, not requiring GCPs enables saving time during the in situ acquisition and during data processing. The method is tested for coastal cliff monitoring, using both a Reflex camera and a Smartphone camera. The quality of the reconstructions is assessed by comparison to a synchronous Terrestrial Laser Scanner (TLS) acquisition. The results are highly satisfying with a mean error of 0.3 cm and a standard deviation of 4.7 cm obtained with the Nikon D800 Reflex camera and, respectively, a mean error of 0.2 cm and a standard deviation of 3.8 cm obtained with the Huawei Y5 Smartphone camera. This method will be particularly interesting when simplicity, portability, and autonomy are desirable. In the future, it would be transposable to participatory science programs, while using an open RTK GNSS network.

A novel strictly anaerobic thermophilic heterotrophic bacterium, strain SLHLJ1(T), was isolated from a Pacific hydrothermal sediment. Cells were Gram-negative coccobacilli (approximately 1.0 × 0.6 μm) with a toga. It grew at temperatures between 33 and 78 °C (optimum 70 °C). Elemental sulphur and L-cystine stimulated its growth. It contained C16:0, C16:1 ω11c, C18:0 and C18:1 ω9c as major fatty acids (>5%), 3 phospholipids and 2 glycolipids as polar lipids. Its DNA G+C content was 43.7 mol%. Phylogenetic analyses based on 16S rRNA gene sequences placed strain SLHLJ1(T) within the family Thermotogaceae. The novel isolate was most closely related to Kosmotoga arenicorallina (97.93 % 16S rRNA gene sequence similarity), K. olearia (92.43%) and K. shengliensis (92.17 %). On the basis of phenotypic, chemotaxonomic and phylogenetic comparisons with its closest relatives, we propose its assignment to a novel species of the genus Kosmotoga. The name Kosmotoga pacifica sp. nov. is proposed with strain SLHLJ1(T) (=DSM 26965(T) = JCM 19180(T) = UBOCC 3254(T)) as the type species.

International audienceThe georeferencing process is crucial to the accuracy of Terrestrial Laser Scanner data, in particular in the context of diachronic studies relying on multi-temporal surveys. The use of Ground Control Points in the georeferencing process can however be complex when confronted with the practical constraints of coastal surveying.A simple and quick alternative method called “pseudo-direct georeferencing” is proposed in the present paper. This method involves internal inclinometers to measure roll and pitch angles and a centimetric GPS to measure the position of the TLS center and the position of one backsight target. When assessing the transformational uncertainty by using a set of independent ground validation points for both classical indirect and proposed pseudo-direct methods, we respectively obtain Root Mean Square errors of 4.4 cm for the indirect method and 3.8 cm for the pseudo-direct metho

A novel hyperthermophilic, piezophilic, anaerobic archaeon, designated NCB100 T , was isolated from a hydrothermal vent flange fragment collected in the Guaymas basin at the hydrothermal vent site named 'Rebecca's Roost' at a depth of 1997 m. Enrichment and isolation were performed at 100 C under atmospheric pressure. Cells of strain NCB100 T were highly motile, irregular cocci with a diameter of~1 µm. Growth was recorded at temperatures between 70 and 112 C (optimum 105 C) and hydrostatic pressures of 0.1-80 MPa (optimum 40-50 MPa). Growth was observed at pH 3.5-8.5 (optimum pH 7) and with 1.5-7 % NaCl (optimum at 2.5-3 %). Strain NCB100 T was a strictly anaerobic chemo-organoheterotroph and grew on complex proteinaceous substrates such as yeast extract, peptone and tryptone, as well as on glycogen and starch. Elemental sulfur was required for growth and was reduced to hydrogen sulfide. The fermentation products from complex proteinaceous substrates were CO 2 and H 2 . The G+C content of the genomic DNA was 41.3 %. Phylogenetic analysis of the 16S rRNA gene sequence revealed that strain NCB100 T belongs to the genus Pyrococcus, showing 99 % similarity with the other described species of the genus Pyrococcus. On the basis of physiological characteristics, DNA G+C content, similarity level between ribosomal proteins and an average nucleotide identity value of 79 %, strain NCB100 T represents a novel species for which the name Pyrococcus kukulkanii sp. nov. is proposed. The type strain is NCB100 T (=DSM 101590 T =Souchoth eque de Bretagne BG1337 T ). †Present address:

Precise underwater geodetic positioning remains a challenge. Measurements combining surface positioning (GNSS) with underwater acoustic positioning are generally performed from research vessels. Here we tested an alternative approach using a small Unmanned Surface Vehicle (USV) with a compact GNSS/Acoustic experimental set-up, easier to deploy, and more cost-effective. The positioning system included a GNSS receiver directly mounted above an Ultra Short Baseline (USBL) module integrated with an inertial system (INS) to correct for the USV motions. Different acquisition protocols, including box-in circles around transponders and two static positions of the USV, were tested. The experiment conducted in the shallow waters (40 m) of the Bay of Brest, France, provided a data set to derive the coordinates of individual transponders from two-way-travel times, and direction of arrival (DOA) of acoustic rays from the transponders to the USV. Using a least-squares inversion, we show that DOAs improve single transponder positioning both in box-in and static acquisitions. From a series of short positioning sessions (20 min) over 2 days, we achieved a repeatability of ~5 cm in the locations of the transponders. Post-processing of the GNSS data also significantly improved the two-way-travel times residuals compared to the real-time solution.

<p>The FOCUS project funded by the European Research Council aims at monitoring deformation across an active submarine fault with an optical fiber using laser reflectometry. To calibrate the measured strains in an absolute reference frame, such as the International Terrestrial Reference Frame (ITRF), a network of eight seafloor geodetic stations was deployed on both sides of the cable and fault. The fault (North Alfeo) is located at the foot of Mount Etna collapsing slope, offshore Sicily, and shows evidence of right-lateral strike-slip in the order of 2 cm per year.</p><p>To locate the acoustic beacons relative to the ITRF, we use a GNSS/Acoustic positioning method. Its principle is to jointly acquire positions of a surface platform relative to the GNSS and, acoustically, relative to the beacons on the seafloor. Positioning a set of beacons over the years should yield their absolute displacement. The optical cable and geodetic stations were deployed in October 2020 at a depth of ~1850m. The first set of GNSS/A data was acquired in August 2021. The next set will be collected in July 2022.</p><p>GNSS/A positioning of acoustic beacons on the seafloor within 1 cm is a challenge. The lever arm between the GNSS and acoustic antennas on the surface platform must be precisely known; the motion of the platform (i.e. antennas) must be precisely monitored. Then, in addition to reducing the uncertainties in GNSS positioning, an acquisition strategy must be designed to minimize the uncertainties in the acoustic ranging data, due to the unknown sound-speed field in the water column and its variability during the ranging sessions (5-6 hours).</p><p>To address these challenges, we used an Autonomous Surface Vehicle (ASV) equipped with a GNSS antenna, an ultra-short acoustic baseline (USBL) transponder coupled with an inertial system (INS). The ASV (3m x 1.60m) has the advantage of being very maneuvrable, acoustically silent (electric power), and compact (reduced lever-arm between antennas). Instead of positioning a single beacon (e.g. boxin), we positioned the ASV relative to several beacons at once and tested different trajectories: quasi-static stations of the ASV (within few meters) at the barycenter of 3 beacons, or series of straight profiles equidistant to pairs of beacons. In addition, while the ASV was acquiring GNSS/A data, a series of vertical temperature/pressure/salinity (CTD) profiles was acquired from the support vessel (R/V Tethys II) to monitor changes in the sound-speed.</p><p>Here we discuss the first results in processing these data and the ensuing uncertainty on the positioning. The GNSS data are reprocessed using Precise Point Positioning (PPP) with Ambiguity Resolution (AR). The improved navigation is then reprocessed with the INS data to obtain a precise position of the USBL center of mass. Then the acoustic ranging data can be merged with the sound-speed information to locate the beacon barycenter, using a least-squares inversion.</p>